A "straight" guy or girl who ends up making out with/sleeping with someone of the same sex after too much booze. The next day invariably features a variation of "Man, I was so drunk, I didn't know what I was doing!"/"Hey, don't read too much into it - I was off my tits!" or just a complete denial of such an incident.
Probably a pun on or reference to the term bottle blonde. The term isn't exclusive to alcohol, and can apply to being high on weed or e.

Yeah, I went home with that bloke last night and the next morning he tried to explain it all away - typical bottle bisexual!